<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>上标与下标</title>
</head>
<body>
  <h1 align="center">上标和下标标签</h1>
  <h3 align="center">上标: x<sup>3</sup>+9x<sub>2</sub>-3=0</h3>
  <h3 align="center">下标: 3x<sub>1</sub>+2x<sup>2</sup>=10</h3>
</body>
</html>